This disclosure relates to gas turbine engines, and more specifically a squeeze film damper bearing assembly for a gas turbine engine.
Squeeze film damping can be used in a bearing assembly that supports a rotatable compressor or turbine shaft of a gas turbine engine. The bearing is contained within a stationary housing. A bearing centering spring, or squirrel cage, within the stationary housing supports the bearing. The squirrel cage is connected to the stationary housing such that the squirrel cage does not rotate relative to the stationary housing but is flexible enough to bend in response to the loads from the bearing. A film of liquid, such as oil, is supplied to an annulus between the stationary housing and the squirrel cage. When the compressor or turbine shaft rotates, unbalanced loads can cause excessive vibration in the shaft. As the bearing moves with the rotation of the shaft, the squirrel cage vibrates or whirls within the stationary housing and squeezes the oil in the annulus, which dampens the vibration of the shaft.
The squirrel cage includes grooves for piston rings, which create a seal between the squirrel cage and the stationary housing to contain the oil in the annulus between the squirrel cage and the stationary housing. The piston rings are split so that the piston rings can be installed in the grooves on the squirrel cage. The oil in the annulus leaks out through the gaps between the ends of the piston rings and more oil is supplied to the annulus. When the squirrel cage vibrates or whirls, the piston rings can rotate in their grooves and the corners of the ends of the piston rings can wear or machine a groove into the bore of the stationary housing or the grooves of the squirrel cage, causing the squeeze film damper to no longer function properly.
In order to prevent the piston rings from wearing a groove into the bore of the stationary housing, a sleeve of wear-resistant material can be placed in between the squirrel cage and the stationary housing such that the stationary housing is not worn when the piston rings rotate. However, the sleeve adds weight and consumes radial space, limiting the ability to fit the necessary hardware with proper cross sectional thickness to avoid part failure. Another option is to drill holes through the hoop of the squirrel cage and attach pins that fit into the gaps between the piston rings to prevent the piston rings from rotating. However, adding holes through the squirrel cage for the pins creates a stress riser in an already highly-stressed part. The squirrel cage may not be able to be made thick enough to deal with the stress concentration due to lack of radial space.